Recent laboratory work on locusts has shown that they can be turned from their harmless “solidarious” phase to a predatory “gregarious” one simply by tickling their hind legs with a paintbrush. Something similar happens with invitations to big art shows. As soon as those little slips arrive in the mail, the art world feels a tickling in its rear. Within 15 minutes of the official opening of “Primavera 2005”, at Sydney’s Museum of Contemporary Art, the place was packed: an orgy of designer clothes and fabulous hair. People were milling about outside, a bouncer guarded the door and gaggles of ticket collectors were pestering the invitees. I jostled about in a pathetic attempt to get a drink before giving up and heading for the art. The gallery was noticeably less crowded than the bar.

Primavera, an annual exhibition for artists under 35, has been running in one form or another since 1992. This year’s guest curator is Felicity Fenner, from the Ivan Dougherty Gallery, and this year’s focus is on “painting”. As if that restriction wasn’t enough already, Fenner settled on a further theme – “the land”. Such a topic runs the risk of being too earnest, or too worthy, a suspicion corroborated by the catalogue essay, which makes clear that the only acceptable positions on “the land” go something like this. Aren’t we degrading the environment? Haven’t we maltreated the original owners? Isn’t it all very confusing? That all of this may be true doesn’t necessarily make it good art. These days, the more that art claims it functions as effective socio-political commentary, the less and less political it seems to be.

Take the work of Monika Behrens. In one painting tanks, choppers, fighter-planes and squadrons of toy soldiers are deployed in desert landscapes, blasting away at bunches of roses; in another John Howard merges into Mr Sheen in a Toytown garnished with barbecue snags; and in yet another Captain America menaces a couple of hooked prawns with a Cuban cigar. Behrens is technically accomplished – take a squizz at the flower petals – but calling a painting “Guantanamo” or saying the prawns “represent David Hicks and Mamdouh Habib” verges on the bathetic.

The restriction to painting poses difficulties too, defying the expectations of the museum’s young audience who are more used to allusive multi-channel video projects than static daubings on canvas. For the MCA’s Jasmine Stephens, this is a good thing: painting should be considered as contemporary as a multimedia installation. Julian Pefanis, chair of art history and theory at Sydney University, seems less convinced: “Once you’re stuck with the medium, you’re going to get [Gerhard] Richter, [Anselm] Kiefer and magic realism. Art abhors a vacuum, so when there’s nothing new you’re just going to get the old stuff repeating – again and again.”

In a way he’s right: you can immediately spot the influences in the work of Tom Müller, Madeleine Kelly, Jemima Wyman and Fiona Lowry. In another way he’s not. The various restrictions imposed – Australian, under-35, painting, land – have not unduly inhibited the range of artists or variety of works. Müller, who is originally from Switzerland, and whose work examines the vicissitudes of globalisation, even got himself naturalised so he could take part. After all, what’s blood, soil, nation, language or culture when you’ve got your career to consider?

This is the first year indigenous artists have been included at Primavera. One Aboriginal community responded to Fenner’s quest with the words: “Over 75, no problem; under 35, hard.” Yukultji Napangati shows it isn’t impossible. Napangati, at age 14, was one of the people who famously walked out of Western Australia’s Gibson Desert with her family in 1984, having never previously encountered white Australia. She works with an extraordinarily intricate and intestinal acrylic dot-line over a red or black ground, a kind of Bridget Riley meets Keith Haring in the Western Desert. Danie Mellor’s slip-cast earthenware shields resemble riveted scraps of airplane crash detritus, scored with fragments of letters: “GRMY”, “MBRI”, “JRR”. Then there’s Pedro Wonaeamirri’s striking ochre-on-linen designs and pukamani poles – most striking, perhaps, in that they are produced either for Tiwi Island funeral rituals or for the global art market. There’s nothing quite like getting a death-pole for your dining room.

I wandered about, chatting to people who were forever keeping one eye out for someone more important to turn up. Conversation tended to be abrupt, volatile. One observer described Müller’s “The Life of Clouds” – an ascending sequence of planks of composition board greyed with acrylic – as something an architect might use to jazz up a corporate lobby. Another snidely said of Lowry’s work: “How many bits of brush can you get into a painting?” It’s a fair comment. The surfaces are speckled with brush-hair, dirt and tiny runs of paint. Lowry is attempting to recreate crime scenes, such as the backpacker murders in the Belanglo State Forest, but I’m not sure she succeeds. “Felony”, one of Howard Arkley’s incredible monochromes, is currently on display upstairs at the MCA, and you can see how Lowry is still struggling to evade Arkley’s aesthetic powers by upping the macabre quotient.

Kelly’s charming pieces are populated by animal-headed creatures. In one painting, dog-headed humanoids in natty beige suits try to revive a man lying prone beneath a yellow sky scarred with sharp-edged birds. In another, mystical stag-headed figures in white robes make a hooded, tattooed dude levitate. Perhaps the most intense work belongs to Michelle Ussher, who provides the show’s only real installations. Ussher typically uses a combination of watercolour and pencil on paper, mixing eerie camping-snap content with an insidiously beautiful technique. Chinoiserie pots, containing living plants, hold down a sloping shelter made from a green blanket and roofed with hessian. There are a couple of nice wooden chairs to sit on. One long wall is covered with six sheets of paper, carefully linked together, on which Ussher has constructed a weird fantasy garden of impossible plants. In another work, drawn straight onto the MCA wall, a silhouetted man abseils from the green web of a six-eyed spider; meanwhile a small bird escapes the clutches of a yellow-feathered dinosaur and another monster spider rears up above, menacing a cute wide-eyed tree creature.

The show continues in Sydney until November 13, then tours Muswellbrook, Geelong, Alice Springs and Tamworth. Admission is free, courtesy of the sponsor, a fact museum-goers are reminded of by a giant banner bearing the slogan: “Free admission – thanks Telstra!” It’s terrific, of course, that people don’t have to pay to get in. But if Telstra was a person, you’d have to say there was something almost psychotic about somebody telling you that they’ve already thanked themselves on your behalf.

I ended up crowding onto the balcony with hundreds of others, most of them smoking. People yelled to make themselves heard and an old guy in an expensive suit swigged alternately from his two glasses of red wine. Earlier that day I had watched a Mike Parr video called “100 Breaths”, in which Parr stands before a camera, a sheaf of 100 of his own self-portraits before him. He brings one self-portrait to his face, holds it there momentarily with a breath, then takes it down and repeats the process with the next sheet. The camera swings in towards his papered face as he inhales, then out again as the sheet comes off. Parr becomes more and more puffed, less and less at ease.

Thinking about it that night, one of Parr’s messages became clear: it’s hard to keep sucking. Locust swarms, having devastated the landscape, invariably either die from starvation or drown when blown out to sea. For my part, I was eventually swept up in a storm of artists, curators, and assorted hangers-on, then blown off elsewhere for a drink.